Chronic viral infections can lead to death if the virus is HIV, or even if the virus is usually innocuous but the person becomes immunosuppressed from another viral infection or treatment for cancer. Previous studies in our lab showed that regulatory T cells (Tregs) can contribute to the establishment of chronic infections by suppressing anti-viral CD8+ T cell responses. These studies were done in mice infected with Friend retrovirus and subsequently shown for HIV and other viruses as well. In this reporting period we provided direct proof using conditional knockout mice that Tregs suppressed CD8+ T cell responses leading to higher virus loads. By reducing levels of Tregs we were able to restore CD8+ T cell responses and decrease chronic virus loads. This knowledge is important because it indicates a possible new therapeutic intervention for chronic infections such as HIV.